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Variability in infaunal bivalve abundance in the Wadden Sea is largely determined by recruitment variability. Post-settlement, but pre-recruitment bivalve mortality is high and related to the occurrence of their most abundant predator, the brown shrimp Crangon crangon. To investigate if the mortality patterns of newly settled bivalves can be explained by the foraging behavior of brown shrimp, we carried out experiments on shrimp functional response to three size classes of juveniles of the Baltic Tellin Macoma balthica. The functional response curves for all three prey sizes (0.62 mm, 0.73 mm, and 0.85 mm) were the hyperbolic Holling's type II. The attack rate was highest for the smallest prey size (a=0.31, medium and large prey a=0.22); the handling time was longest for the largest prey size (T

Ongoing statistical sophistication allows a shift from describing species' spatial distributions toward statistically disentangling the possible roles of environmental variables in shaping species distributions. Based on a landscape-scale benthic survey in the Dutch Wadden Sea, we show the merits of spatially explicit generalized estimating equations (GEE). The intertidal macrozoobenthic species, Macoma balthica, Cerastoderma edule, Marenzelleria viridis, Scoloplos armiger, Corophium volutator, and Urothoe poseidonis served as test cases, with median grain-size and inundation time as typical environmental explanatory variables. GEEs outperformed spatially naive generalized linear models (GLMs), and removed much residual spatial structure, indicating the importance of median grain-size and inundation time in shaping landscape-scale species distributions in the intertidal. GEE regression coefficients were smaller than those attained with GLM, and GEE standard errors were larger. The best fitting GEE for each species was used to predict species' density in relation to median grain-size and inundation time. Although no drastic changes were noted compared to previous work that described habitat suitability for benthic fauna in the Wadden Sea, our predictions provided more detailed and unbiased estimates of the determinants of species-environment relationships. We conclude that spatial GEEs offer the necessary methodological advances to further steps toward linking pattern to process.

The link between biodiversity and ecosystem functioning is an important question that remains unresolved, particularly in marine systems, in which cycling of organic matter by benthic organisms is of global significance. Direct observations of specific resource use by each species in single- and multispecies communities, as quantified by stable isotopes, facilitates a mechanistic understanding of the importance of each species for ecosystem functioning. We tested the effects of altered biodiversity (species richness) of deposit-feeding macrofauna on incorporation and burial of phytodetritus in combinations of three species representing natural communities found in the sediments of the species-poor Baltic Sea. The three species, two amphipods and a bivalve, had different rates of incorporation and burial and different needs for carbon (C) and nitrogen (N). The amphipods exhibited clear resource partitioning in sympatry, as a result of vertical separation in the sediment and consequent differential use of food. Communities of several species incorporated more C and N than expected from the respective single-species treatments, due to higher incorporation by surface feeders in multispecies treatments. Community incorporation of N in the most diverse treatment even exceeded N incorporation by a single-species treatment of the best-performing species, showing transgressive over-yielding. This over-yielding was primarily due to positive complementarity in all treatments. Diverse soft bottoms are also likely to be more productive in the long run, as species-specific traits (subsurface feeding) preserve fresh phytodetritus by burying it to depths in the sediment at which the mineralization rate is low. The more diverse sediment communities showed more efficient trophic transfer of phytodetritus, a finding of general significance for understanding biological processes driving the transformation of nutrients and energy in benthic ecosystems.

We conducted a survey to provide knowledge on mechanisms controlling spatial and temporal variability of macrobenthos in an intertidal Wadden Sea area partly covered by invasive Spartina anglica. Benthic macrofauna was collected seasonally at seven stations along a transect covering non-vegetated mudflat and vegetated marsh areas. Shannon diversity index was consistently higher for macrobenthos in the open mudflat compared to the marsh area. Infaunal species, like Arenicola marina, Tubificoides benedeni and Macoma balthica, were more abundant in the mudflat than the marsh, while the opposite was evident for epifaunal species, like Hydrobia ulvae and Littorina littorea. The infaunal crustacean, Corophium volutator, on the other hand, appeared particularly attracted to the mudflat–marsh boundary. The biomass of below-ground plant materials and macrodetritus was positively correlated with the total macrofaunal abundance, while the biomass of dead below-ground plant materials alone showed a significant negative correlation with infaunal abundance. Total macrofaunal abundance was highest during summer in the mudflat, while no seasonal pattern was evident in the marsh. The negative influence of S. anglica invasions on infaunal abundance may have serious implications for higher trophic levels, such as waterbirds, that forage in Wadden Sea areas and thus for the overall biodiversity and ecosystem functioning.

The first occurrence and presence of the bivalve Macoma balthica in the Pleistocene shallow marine sediments (Crags) of East Anglia has long been used to characterise the youngest “Weybourne” or “Wroxham” Crag Formation of Early to early Middle Pleistocene age. A review of recent work on the morphological variation and genetic lineages of living populations of the species and of work on fossil discoveries in East Greenland suggests that the current palaeontological species definition is too narrow, that the species arrived in the Atlantic about 2.4 Ma and much earlier than is envisaged from the studies of the North Sea Basin, and that there were several trans-Arctic migrations of the species during the Pleistocene. This paper reviews these findings and concludes that: (i) detailed morphometric analyses of fossil Macoma species from the Crag need to be undertaken and the species definitions comprehensively reviewed to take account of the morphological and genetic variation seen in modern populations; (ii) detailed morphometric analysis of modern M. balthica should be undertaken and tied to the different genetic lineages, and (iii) the current palaeontological definition of Macoma balthica should not be relied on as the basis for a First Appearance Datum (FAD) in the Southern North Sea basin.

The world's largest brackish water sea area, the Baltic Sea, is considered to be one of the most polluted seas of the world. Many new pollutants are constantly entering the environment, such as brominated flame-retardants (BFRs). BFRs represent a group of compounds that structurally resemble hydrophobic organic contaminants, but only scarce data about their toxicity to marine organism exist. Thus, the purpose of this study was to analyze long-term in vivo cytotoxicity and genotoxicity of hexabromocyclodododecane (HBCDD) to exposed marine invertebrates using a suite of cytogenetic biomarkers. This included a set of nuclear and nucleolar characteristics and the micronucleus test. The use of those parameters reflects different mechanisms of nuclear activity regulation in cells (as a parameter of cytotoxicity) and measures subcellular processes. The induction of nuclear abnormalities (like the formation of micronuclei) was also employed here as a parameter of genotoxicity. In order to reflect the proliferative and metabolic activity of the cells the number of argylophillic nucleolar organiser regions (NORs) in interphase cells was scored. Over a period of 50 days an in vivo exposure experiment with a clam Macoma balthica and different concentrations of HBCDD (nominal concentrations of 0, 100 and 250microg/l) with three replicates each was performed. Gill cells were used as "sentinel systems" considering specificity in metabolism, repair mechanisms, adaptative response and cell proliferation. A significant increase in nuclear and nucleolar abnormalities and in the frequency of dead cells was observed during the duration of the experiment with the highest peak occurring 10 days after exposure for nuclear abnormalities and 20-30 days after exposure for malfunction of ribosomal genes (NORs) (GLM analyses and Spearman correlation, p

Recent reductions in sea ice cover and thickness in the Arctic will lead to changes in food supplies for benthic consumers. We experimentally assessed responses of two common Arctic macrobenthic species, Macoma balthica (Bivalvia) and Monoporeia affinis (Crustacea) from Kotzebue Sound (Alaska, USA) to varying food materials (phytoplankton and ice algae). Phytoplankton and 13C-labelled ice algae were added separately or together to pre-sieved sediment cores containing known numbers of Macoma or Monoporeia. After 8 d, sediments and animals were analyzed for bulk C/N contents, isotopic signatures, fatty acid compositions and compound-specific δ13C values. Our results showed that the two species responded differently to varying food materials. Loss of characteristic fatty acids and changes in δ13C values in the surrounding sediments indicate that Macoma preferentially consumed ice algae compared to phytoplankton, while Monoporeia non-selectively ingested both food materials. Feeding behaviors also differed between the two species: Macoma fed primarily on material from the sediment surface, and did not appear to mix material to depth, while Monoporeia mixed some fresh food material from the surface down to subsurface sediments (1–2 cm). Analysis of animal biomass showed more 13C-labelled organic carbon from ice algae was assimilated by individual Macoma compared to individual Monoporeia. Moreover, δ13C values of fatty acids in Macoma were much higher than those in Monoporeia, suggesting that Macoma directly assimilates fatty acids from their food source while Monoporeia might de novo biosynthesize fatty acids in their biomass. Additionally, both species had higher fatty acid contents and proportion of polyunsaturated components when they fed on ice algae compared to phytoplankton, implying that ice algae may be a better food than phytoplankton for Arctic benthos. Finally, analysis of bacteria-specific fatty acids in sediments (from both types of animal cores) showed that the δ13C values were enriched up to 400‰ relative to natural background values (−25% to −30‰), suggesting that organic carbon from fresh ice algae could be rapidly incorporated into bacteria biomass. The collective results of this experimental study suggest that the changes in food supplies due to reduction of ice coverage will have a greater impact on those benthic organisms that prefer ice algae to phytoplankton. This may lead to the potential changes in community structure favoring those organisms that can best utilize the fatty acids contained in both phytoplankton and ice algae.

We experimentally reduced benthic microalgae using opaque rubber canopy covers and observed dietary responses of Corophium spinicorne (amphipod) and Macoma balthica (bivalve) based on δ 13 C and δ 15 N measurements in 2 estuarine tidal flats. Each of the tidal flats (MA and TE) was predominated by marine- or terrestrial-origin organic matter (OM), respectively. We hypothe- sised that the reduction of benthic microalgae correspondingly decreases the proportion of mac- robenthos diet attributable to benthic microalgae, and enhances their assimilation of allochthonous OM. Our canopy treatment reduced chlorophyll a in the surface sediment by 35 to 40%. While δ 13 C and δ 15 N of M. balthica were not affected by the canopy treatment, the signatures of C. spinicorne were significantly altered at both sites. In MA, the canopy treatment reduced the nutritional depen- dence of C. spinicorne on benthic microalgae and maintained their substantial dependence on the marine-origin OM predominating in the sediment. On the contrary, in TE, the canopy treatment enhanced the nutritional dependence of C. spinicorne on benthic microalgae and lowered their dependence on the terrestrial-origin OM predominating in the sediment. The canopy treatment sig- nificantly changed the C:N and δ 15 N of the sediment OM in TE. This suggests that benthic micro- algae affected biogeochemical processes and the chemical properties of OM in the sediment subsur- face. Benthic microalgae may have indirectly controlled nutritional utilisation of terrestrial-origin OM in the sediment by macrobenthos. Overall, the dietary compositions of macrobenthos did not always vary in proportion to the relative abundance of OM sources; the chemical properties of allochthonous OM, its biogeochemical alterations and species-specific food selectivity are also important factors.

The interaction of prey distribution patterns and predator behavior can mediate preda- tor-prey dynamics. Inter-patch distance (lag) may be especially important in the interacting effects of aggregation and interference among predators on their search and prey-handling ability. Interac- tions of blue crabs Callinectes sapidus preying upon thin-shelled clams Macoma balthica in Chesa- peake Bay provide a test of how the opposing forces of aggregation and interference interact with the spatial distribution of prey patches to influence rates of prey consumption. Blue crabs can detect clam patches from up to 15 m away using chemosensory cues, and they aggregate on them, thus facilitat- ing predation, but exhibit agonistic behaviors when closer than 5 m to another crab, thus reducing feeding efficiency. We used these patterns of aggregation and interference to modify a generalized functional response model to describe individual crab foraging efficiency as a function of distance between patches. The model predicted highest predation rates at an intermediate lag of 6.6 m. We tested this a priori hypothesis with a set of field experiments wherein prey patches were established with lags of 1, 7, 10, and 50 m. Predation rates were highest at intermediate lags, as predicted. This work highlights the importance of the interaction between spatial scales and ecological processes, demonstrating that spatial heterogeneity is not noise that obscures processes, but an active compo- nent of the predator-prey dynamic.

Many terrestrial habitats, and certainly man-made systems such as woodland and agricultural habitats, are characterised by a mosaic of different habitat types. In contrast, most seafloors have a rather uniform visual appearance which is enhanced by the cryptic nature of many of their inhabitants. The present study aimed to: (1) describe landscape scale spatial patterns of benthic infauna after evaluating 3 methods for analyzing auto correlations (Moran's I, semivariance and fractals), (2) compare the benthic patterns with patterns described for other organisms, and (3) highlight shared characteristics. During 4 consecutive years (2002 to 2005) we assessed spatial structuring of 4 intertidal benthic invertebrates (Cerastoderma edule, Macoma balthica, Nereis diversicolor and Nepthys hombergii) in the Wadden Sea, The Netherlands. We annually sampled similar to 2750 stations based on a 250 m grid, covering an area of ca. 225 km(2). On the basis of simulated spatial distributions, we selected Moran's I to analyze spatial patterns for the following reasons: (1) due to standardization, results can be directly compared, (2) Moran's lis the least difficult to evaluate, since it is related to the familiar Pearson's correlation coefficient, and (3) significance can readily be assessed. The 4 benthic species were all spatially structured at the landscape scale, with spatial features being smaller than the physical structure of the intertidal environment, i.e. the intertidal extent. During the 4 yr, some species changed their distribution, but spatial characteristics, i.e. patch size and amplitude of autocorrelation, remained similar. Higher overall density resulted in stronger autocorrelation with no differences between species. A comparison between spatial structuring of benthic fauna with patterns encountered in other habitats, whether marine or terrestrial, was unsuccessful due to differences in extent and grain. We argue that future research should focus on spatial structure in species' distributions as an ecological relevant parameter.

Burrowing bivalves are associated with particular sediment types within sedimentary systems. The degree to which bivalve sediment associations are repeatable across systems has seldom been investigated. To investigate whether such repeatability exists across tidal flats, we compared adult and juvenile distributions of 3 bivalve species (Cerastoderma edule, Scrobicularia plana, Macoma balthica) across 6 European tidal flats. Across systems, the adult bivalves showed fairly repeatable distributions, with C. edule occurring in sandy sediments and AT balthica and S, plana occurring in muddy sediments. Exceptions were observed in systems composed primarily of muddy sediments (Aiguillon Bay and Marennes-Oleron Bay) and the Dutch Wadden Sea. Interestingly, juveniles and adults of C. edule and S. plana showed similar distributions across systems, M. balthica juveniles and adults showed habitat separation in 3 of the 6 studied systems; in 2 of these, it has been shown previously that juvenile M. balthica settle in mud at high tidal levels and migrate to lower sandier flats later in life. The high occurrence of juvenile M. balthica towards high sandy flats in Mont Saint-Michel Bay suggests that juveniles might choose high tidal fiats rather than muddy sediments per se. A repeatable association in adults and juveniles with respect to sediment could Suggest that juveniles actively settle in the proximity of the adults and/or that juveniles settling away from the adults incur a higher mortality due to either predation, physiological stress, or other factors.

Maximum depth of occurrence and preferred substrata have been determined, and distribution maps prepared for four bivalve species of the S Baltic: Cerastoderma glaucum (Poiret) (30–35 m, sandy bottom), Macoma balthica (L.) (55–80 m, muddy bottom), Mya arenaria L. (30–35 m, sandy bottom) and Mytilus edulis L. (40–50 m, stony bottom); four bivalve communities have been distinguished and mapped.

We performed a 4 wk laboratory experiment with the semi-motile burrowers Macoma balthica and Marenzelleria spp. and the motile surface sediment stirrers Monoporeia affinis and Mysis mixta to study their effects on the transport of tracer particles (mean diameter () 1 µm) in the sediment, sediment parameters (depth of the oxidized layer, water content, organic matter content), water turbidity, and nutrient fluxes across the sediment-water interface (PO4 3- , NO2 - + NO3 - , NH4 + ; measured weekly). Two densities were included for each taxon, representing a low and a high field density. M. balthica significantly increased particle mixing, the rates being 59.6 and 61.9 × 10 -3 cm 2 d -1 . While all taxa increased turbidity in the overlying water, the strongest effects were caused by M. affinis and M. mixta, resulting in 112- and 45-fold increases, respectively. In addition, these 2 motile species increased oxidation of the sediment surface layers. A distinctive difference in the nutrient fluxes was observed between the semi-motile (M. balthica, Marenzelleria spp.) and the motile taxa (M. affinis, M. mixta). The former increased the efflux of both PO4 3- and NH4 + , while the latter sup- pressed the efflux of NH4 + and decreased the sediment uptake of NOx, indicating enhanced N removal. Higher nutrient exchange rates were observed at the higher animal densities. We conclude that a shift in the benthic communities from the 2 motile to the 2 semi-motile taxa, observed through- out the northern Baltic Sea, may notably alter the regime of benthic nutrient cycling and thereby the performance of the entire ecosystem.

We studied the effect of crustacean predators on native/non-native Macoma balthica bivalves in aquarium experiments. North Sea M. balthica (NS Macoma) were recently observed in the southern Baltic Sea. They differ genetically and in terms of morphology, behaviour and evolution- ary history from Baltic Sea M. balthica (BS Macoma), and this may affect predation pressure and community structure. We hypothesised that predators consume more of the prey they co-exist with. NS Macoma and BS Macoma were exposed to crustacean predators common in the North Sea (Carci- nus maenas and Crangon crangon) and in the Baltic Sea (C. crangon and Saduria entomon). Contrary to our hypotheses, the North Sea predators ate more BS Macoma, and S. entomon ate more NS Macoma. The crush-limited C. maenas preyed more on globular BS Macoma, whereas S. entomon, which do not crush but pry open the bivalve shell, ate more NS Macoma, which have a lighter (thus probably thinner) shell than BS Macoma. When NS and BS Macoma were offered together, BS Cran- gon ate more NS Macoma. We also studied BS Crangon consumption of M. balthica to assess whether sizes offered fall within the size spectrum that C. crangon can eat. Small (20 to 40 mm long), medium (40 to 50 mm) and large (50 to 60 mm) C. crangon especially ate small M. balthica. Differences in shape, size and meat/shell weight ratio between the BS and NS Macoma partly explained the differences in the susceptibility to predation by native and non-native predators.

Most benthic invertebrates and plant species that survive in the brackish Baltic Sea are characterized by populations in which growth is reduced and genetic diversity is low, indicating that these species live under marginal conditions. In this study, we tested for a salinity-related growth rate reduction in 21 European Macoma balthica populations. Additionally, we transplanted clams into hyposaline environments, along the Baltic Sea salinity gradient, and compared survival, growth and condition with control groups. All transplants into hypoosmotic environments were successful. Despite the osmotic shock, the results showed no reduced growth rates in transplanted individuals. Only the clams that had been transplanted into the extremely oligohaline Gulf of Bothnia (0.5-3.0 PSU) exhibited reduced growth rates in comparison to the control group. From this study we conclude that M. balthica has an exceptional capacity to acclimatize to extremely brackish conditions, which may explain its abundance and diversity in the Baltic Sea.

The role of multi-species benthic diatom films (BDF) in the settlement of late pediveliger larvae of the bivalve Macoma balthica was investigated in still-water bioassays and multiple choice flume experiments. Axenic diatom cultures that were isolated from a tidal mudflat inhabited by M. balthica were selected to develop BDF sediment treatments characterized by a different community structure, biomass, and amount of extracellular polymeric substances (EPS). Control sediments had no added diatoms. Although all larvae settled and initiated burrowing within the first minute after their addition in still water, regardless of treatment, only 48-52% had completely penetrated the high diatom biomass treatments after 5 min, while on average 80 and 69% of the larvae had settled and burrowed into the control sediments and BDF with a low diatom biomass (3.5 µg Chl a g1 dry sediment), respectively. The percentage of larvae settling and burrowing into the sediment was negatively correlated with the concentration of Chl a and EPS of the BDF. This suggests higher physical resistance to bivalve penetration by the BDF with higher diatom biomass and more associated sugar and protein compounds. The larval settlement rate in annular flume experiments at flow velocities of 5 and 15cm s1 was distinctly lower compared to the still-water assays. Only 4.6-5.8% of the larvae were recovered from BDF and control sediments after 3h. Nonetheless, a clear settlement preference was observed for BDF in the flume experiments; i.e., larvae settled significantly more in BDF compared to control sediments irrespective of flow speed. Comparison with the settlement of polystyrene mimics and freeze-killed larvae led to the conclusion that active selection, active secondary dispersal and, at low flow velocities (5cm s1), passive adhesion to the sediment are important mechanisms determining the settlement of M. balthica larvae in estuarine biofilms.

Because of its relatively low tolerance to elevated temperatures, Macoma balthica (L.) may be one of the first important marine species in temperate coastal areas to suffer from a warming climate. For the last few decades, the abundance of the species in the Dutch Wadden Sea has been se- riously declining. At lower latitudes, the southern edge of its range recently shifted several 100s of km to the north. To understand changes in abundance related to high temperatures, we studied short-term population responses to warmer than average seasons using data from a long-term (>35 yr) sampling program in the western Wadden Sea. The observed relationships included reduction of reproductive output and recruitment in years starting with mild winter-spring periods, reduction of adult survival in years with warm summers, reduction of annual migration in ~8 mo olds to more favourable areas in mild winters, reduction of growth rates in warmer than average growing seasons, and enhancement of seasonal weight loss in milder than average winters. We conclude that elevated temperatures nega- tively affect population dynamics of M. balthica in a number of ways, i.e. via recruitment or mortality as well as growth. These negative influences were observed already far below the upper lethal tem- perature of the species and in populations living ~1000 km poleward of the warm edge of the species' range. The outcome of M. balthica's energy balance appears to be decisive for their continued exis- tence by effects not only on individual weights but also on mortality as well as reproduction.

We examined how interactions among the three dominant species of the Macoma balthica community in the St-Lawrence estuary influence net biogeochemical fluxes and the composition of the sedimentary bacterial community. We manipulated the biodiversity of the community via combinations of Macoma balthica, Mya arenaria, and Nereis virens in sediment microcosms containing sieved and homogenized tidal-flat sediment. Each combination was adjusted to similar total biovolumes and in situ animal densities. Compared to treatments with single species, which were also adjusted to similar biovolumes and densities, combinations of multiple species changed the fluxes of oxygen, phosphate, ammonium, and nitrate across the sediment-water interface and altered the composition of the microbial community beyond the level predicted by linear addition of the single species effects. Most combinations involved positive interactions that increased net fluxes. Although N. virens dominated system behavior, we also observed positive interactions between the two bivalves, and between N. virens and M. balthica. Weaker interactions, sometimes negative, were observed between N. virens and M. arenaria. Most effects could be directly linked to total oxic sediment volumes and burrow volumes generated by the different species. N. virens had the maximum species-specific burrow volume/biovolume ratio, and its presence maximally impacted fluxes. The principal interactions between species that affect net solute fluxes reflect space occupation, life habit (position, location), and irrigation of burrows. These factors interact with reactive substrate distributions and remineralization patterns to produce particular flux balances. Future studies should include the relationships of biodiversity to spatial scales over which the functional groups are distributed, the volumes actively occupied and irrigated, production rates of burrows, and the depths to which the organisms burrow. 1. Institut des Sciences de la Mer de Rimouski (ISMER), 310 allee des Ursulines, Rimouski (Quebec), Canada, G5L 3A1. 2. Laboratoire de Microbiologie, de Geochimie et d’Ecologie Marines (LMGEM), Centre d’Oceanologie de Marseille (COM), Campus de Luminy, Avenue de Luminy, case 901, 13288 Marseille Cedex 09, France. 3. Present address: Laboratoire des Sciences de l’Environnement Marin (LEMAR), UMR6539 UBO/CNRS/ IRD, Institut Universitaire Europeen de la Mer (IUEM), Technopole Brest Iroise, 29280 Plouzane, France. email: emma.michaud@univ-brest.fr 4. School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, U.S.A. 5. UMR-CNRS 5023, Laboratoire d’Ecologie des Hydrosystemes Fluviaux (LEHF), Universite Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France. 6. Earth & Planetary Sciences, McGill University, 3450 University Street, Montreal (Quebec), Canada, H3A 2A7. Journal of Marine Research, 67, 43–70, 2009

In many European estuaries, extensive intertidal habitats could vanish in the future due to rising sea levels that squeeze tidal flats against established sea defences. The remaining intertidal area is likely to become steeper with coarser sediment, and saline water may intrude upstream due to increased water depth and enhanced wave energy. This paper investigates the impacts of sea-level rise on benthic macrofauna in an intertidal habitat in the Humber estuary, UK. Field surveys were conducted between 2003 and 2004 to examine spatial patterns of benthic macrofaunal biomass along the estuarine longitudinal gradient and the local beach width gradient. Multiple regression analysis revealed that >80% of the observed variation in biomass of the 2 dominant bivalve species Macoma balthica and Cerastoderma edule, and the total biomass of other macrobenthic species, could be explained by key environmental variables such as salinity, sediment characteristics and morphological factors. Physical data for the Humber estuary were assessed to predict the likely course of changes in these key environmental variables in response to sea-level rise. Model simulations showed that a sea-level rise of 0.3 m would result in a 6.7% loss of intertidal area and 6.9% loss of total macrobenthic biomass, and that saline intrusion could partly compensate for such loss of macrobenthic biomass. However, associated environmental changes, such as beach slope steepening and sedimentary shifts, could have overriding negative impacts with potential loss of macrobenthic biomass of up to 22.8%, depending on the extent of environmental changes.

Bioturbating lugworms (Arenicola marina) were excluded from 400 m² plots of intertidal sand which initiated sequences of direct and indirect changes in the structure of the benthic community. The sessile, tube-building species Polydora cornuta and Lanice conchilega took advantage of the absence of lugworms and settled preferentially on lugworm exclusion plots. The protruding tubes provided attachment for an ephemeral development of algal tufts (Berkeleya colonies and Enteromorpha thalli) which in turn enhanced settlement of the juvenile drifting clams Mya arenaria and Macoma balthica. This causal chain of enhanced bivalve settlement in the presence of above-ground structures, like animal tubes and algae, on lugworm exclusion plots occurred in 2 years at different tidal zones with different tube builders, algae and juvenile clams. A significant response of L. conchilega in a year with relatively low lugworm abundances at the entire site suggests that not only the actual absence of large bioturbators was responsible for the establishment of tube-dwelling species, but also a cumulative change of the sediment in exclusion plots since the onset of the experiment. While the sediment on lugworm plots remained permeable, fine particles and organic matter accumulated at exclusion plots. It is suggested that these differences in sediment characteristics were the product of divergent benthic engineering by sediment destabilizing lugworms on control plots and sediment stabilizing species on exclusion plots. Cumulative changes of the sedimentary habitat and cascading effects in the benthic community may explain the persistence of patches that are dominated by either sediment stabilizing or destabilizing species in the assemblage mosaic of intertidal sediments.

Monoclonal antibodies specific to a heat shock protein 70-like protein expressed in the eggs of Macoma balthica (mb-HSP70) were employed to develop an enzyme-linked immunosorbent assay (ELISA) to quantify fecundity in females. The assay was specific to egg tissue, with no demon- strable reactivity with juvenile or male tissues. The concentration of mb-HSP70 increased as the female gonads matured, necessitating the determination of a calibration curve for future experi- ments. The number of eggs in females was positively correlated with body mass index (BMI), and clams with a BMI

We employed the technique of subtractive immunization (SI) to identify specific bio- markers of oocyte development in Macoma balthica. Analysis revealed that 2 novel proteins (45 and 96 kDa) were induced during female gametogenesis that were neither present during other life stages, nor in male clam tissues. A total of 78 viable hybridomas were specific for either the 45 or 96 kD M. balthica proteins. Subsequent peptide fragment analysis of the 96 kDa protein revealed that it was essentially identical (>99.9%) to the evolutionarily conserved heat shock protein 70 family. The resultant hybridomas were screened for their utility in a quantitative capture ELISA configuration. Two antibody systems were designed that allowed the quantification of either the 45 or 96 kDa pro- tein in M. balthica tissue homogenates and are useful for studies on M. balthica gametogenesis and fecundity. Subtractive immunization is a powerful tool, as it simultaneously identifies novel protein targets while producing monoclonal antibodies specific to them.

Adults of the bivalve Macoma balthica live burrowed in mud or sand, which makes their shells invisible so that a vision-related selective advantage of colour morphs is hard to imagine. Nevertheless, this species harbours a conspicuous colour polymorphism of white, yellow, orange and red. Here we present data from laboratory-reared crosses that demonstrate a genetic basis for this colour polymorphism. The results suggest a simple model of inheritance of colour class: four alleles at a single locus displaying linear hierarchy of dominance, in the following order of increasing dominance: white , yellow , orange , red. Shell colour intensity is also shown to be a heritable trait in M. balthica. Furthermore, bicolouration may to a degree be a heritable trait, but the sample size is too small to draw any conclusions about possible inheritance mechanisms. Heritable colour variation can now, with the proposed model, be used as a genetic marker. Furthermore, the proposed model will provide the basis for further analysis of the evolutionary forces maintaining this colour polymorphism that is hidden from view for most of the life of this bivalve.

The effect of severe and moderate hypoxia on food uptake of benthic macrofauna was studied in the laboratory. The hypothesis was that low oxygen concentrations negatively affect feed- ing at oxygen levels that have little effect on the studied animals' survival. The bivalve Macoma balthica, the priapulid Halicryptus spinulosus, the amphipods Monoporeia affinis (subadult & juve- nile) and Pontoporeia femorata (subadult) were offered the 14 C-labelled diatom Skeletonema costa- tum in 0.8 to 10.6 mg O2 l -1 . Feeding was measured as radioactivity uptake. Subadult amphipods were studied one species at a time (single) or together (mixed). Feeding changed in all amphipods at the lowest oxygen concentrations, but no effect was found for M. balthica and H. spinulosus. At the lowest concentration (0.8 mg O2 l -1 ) feeding by subadult M. affinis (single) was only 17% of the full oxygen saturation (10.6 mg O2 l -1 ), and, at 1.6 mg O2 l -1 , 14% of the feeding at 8.9 mg O2 l -1 . Juvenile M. affinis consumed more labelled algae at 3 mg O2 l -1 than at higher oxygen concentrations. M. balthica feeding was not affected. Little radioactivity uptake was registered for H. spinulosus at any oxygen concentration, showing that H. spinulosus is not a surface deposit feeder. The amphipods were the most sensitive to week-long oxygen deficiency. Survival decreased significantly in the lowest oxygen concentrations (0.8; 1.6 mg O2 l -1 ). Of the subadult M. affinis 15 and 65%, respectively, survived, compared with 0 and 58% for P. femorata. Juvenile M. affinis mortality was high in all oxygen concentrations, whereas most M. balthica and H. spinulosus survived.

Ecosystem-level effects of stressors are critical to understanding community regulation, and environmental stress models are useful in describing such effects. Hypoxia is an important stres- sor in aquatic ecosystems that usually decreases abundance and biomass of benthic fauna. In field surveys, predator abundance is low in hypoxic areas, and in lab experiments, predators reduce their feeding rates under hypoxic conditions, leading to the hypothesis that consumer stress models (CSMs), rather than prey stress models (PSMs), apply to the systems. We tested predictions from these models with manipulative field experiments wherein we varied predator access to marked Macoma balthica clams at deep and shallow sites in the York River, Chesapeake Bay, before (June) and during (August) hypoxic episodes. In June, dissolved oxygen in deep and shallow sites was normoxic (>2 mg l -1 ) for most of the experiment. In August, the shallow zone remained normoxic, while the deep zone experienced several hypoxic episodes. During hypoxia, predation rates in hypoxic sites were more than twice those in normoxic sites, whereas mortality due to physical stress did not differ between time periods or depths. Ambient clam densities were lower at the deep sites than at the shallow sites, and in August than in June. We conclude that hypoxia increased the suscep- tibility of benthic prey to predation, enhancing infaunal secondary production available to predators, but concurrently reducing the resilience of the benthic community. These findings are inconsistent with the predictions of CSMs, indicating that PSMs better describe this system.

SUMMARY The food and feeding habits of Shelduck Tadorna tadorna are described, based on the analyses of the viscera of 30 birds collected under special licence, and of 18 birds found dead or dying during the cold weather of 1963, on faecal material from eight incubating birds, on field observations and on the literature. The birds came from a number of different localities and from each month of the year, apart from July. The mollusc Hydrobia ulvae (Pennant) was found in all 46 birds which contained food, and it is quite obvious, and this is confirmed by the literature and by faecal analyses, that this is the most important food item during much of the year and in many different localities. Other species eaten included the bivalve Macoma balthica, the amphipod Corophium volutator, the ragworm Nereis sp., the alga Enteromorpha, and occasionally the seeds of various plants. The importance of H. ulvae is examined in the light of its distribution and numbers, which may be a strong controlling factor in concentrating Shelduck in certain areas at certain times of the year. The feeding behaviour of Shelduck, and a number of other birds, is apparently closely related to the cyclic behaviour pattern of the main food species, H. ulvae. It seems that Shelduck have a rather fixed type of feeding behaviour which exploits only one feeding niche and therein mainly one food item. Any event (prolonged gales or very cold weather) which prevents the bird from using that niche can be the cause of heavy mortality.

This experimental study examined the interactive effects of bioturbation and settling organic matter (OM) on the fate (burial and remobilisation) of 2 surface-deposited contaminants in Baltic Sea s ...

Declining populations of the blue crab, Callinectes sapidus, may be suitable for enhancement with hatchery-reared juveniles. Fo r three years, field experiments were conducted to determine if shallow, unvegetated, marsh-fringed nursery habitats in lower Chesapeake Bay are below carrying capacity and thus capable of supporting additional juvenile crabs. The field experiments included sampling of wild and hatchery-reared juvenile blue crabs and their major benthic prey, and manipulative experiments to assess the survival of juvenile crabs and the abundance of benthic prey in enhanced and control coves. Densities of the clam Macoma balthica ,a major prey of the blue crab, were initially high in enhanced coves and decreased to a level equivalent to that in control coves by the end of the experiment, but always remained well above a low-density threshold. Survival of juvenile crabs was lowest where clam densities were highest, suggesting that alternative prey did not deter predation on juvenile crabs, but instead led to higher densities of cannibalistic crabs through bottom-up control. Crab densities correlated with densities of major benthic prey and prey density never dropped below a low-density threshold. Marsh-fringed nurseries are apparently below carrying capacity for the blue crab and could be enhanced through the release of hatchery-reared juveniles.

Species loss or gain can change ecosystem functions according to the ecological context (e.g. assemblage composition, habitat heterogeneity and disturbance regime). We document how the suspension-feeder cockle Cerastoderma edule (L.) affects some properties of intertidal sediments during macrofauna recovery after deliberately induced anoxia. Forty adult cockles were transplanted to each of 12 plots (25 × 25 cm) in 3 physically homogeneous patches (4 × 4 m). Two patches had recolonised for 4 or 7 mo (DJ and DM, respectively) and had a very similar number of species (DJ: 4.5 ± 0.3 and DM: 5 ± 0.0). The other patch (C) was natural sediment with a relatively high species diversity (6.5 ± 0.6). Species composition was different among the 3 patches (DJ < DM < C) and indicated an increasing number of individuals and functional groups in accordance with the duration of the recovery period (DJ < DM < C). Changes in abundance of the resident macrofauna, in total benthic mineralization rates (oxygen uptake and carbon dioxide release) and in the exchange of inorganic nitrogen at the sediment–water interface were compared between transplanted and undisturbed plots. The functional response of the sediment ecosystem to the gain of C. edule varied among the patches. Following C. edule addition, ammonium release increased 3 to 4 times in the sediment which had been recolonising for 7 mo (DM), while uptake of nitrate decreased at similar levels in the other 2 patches (DJ and C). Effects were related to variations in the densities of 2 species, namely new recruits of the surface deposit-feeder Macoma balthica (=5 mm) and the surface-detritivore and bioirrigator Hediste diversicolor. Cockles caused a decrease in the densities of M. balthica (=5 mm) and an increase in those of H. diversicolor, mainly in DM. Cockles also modified how densities of these species and of Heteromastus filiformis correlated to sediment–water exchanges of ammonium and oxygen. C. edule also enhanced oxygen uptake at all sites, mainly due to its specific respiration rate. Variability in the functional response among patches of habitat (e.g. context-dependence) resulted as a consequence of biotic interactions between the cockles and the resident infauna.

6 pages, 1 table, 2 figures, A comparative survey of the anaerobic survival potential of four different bivalve species and the interference of associated bacteria has been carried out. Individuals from both subtidal and intertidal environments were considered by selecting the following species: Mytilus edulis (subtidal epifaunal), Spisula subtruncata (subtidal infaunal), Macoma balthica (intertidal infaunal) and Cerastoderma edule (intertidal infaunal). Anaerobiosis was simulated in the laboratory by subjecting individuals to the following conditions: nitrogen atmosphere, air atmosphere and anoxic seawater incubation. Moreover, the effect of the antibiotic CA (chloramphenicol) was investigated, either as a pre-treatment of individuals kept under normoxic conditions for a week or directly added to the anoxic incubation media. According to survival performances of the individuals, intertidal animals that use to cope with tidal fluctuations in the coastline (emersion processes) had an extraordinary greater capacity to survive aerial exposure as compared to both nitrogen gas and anoxic seawater incubations most likely due to their capacity to perform aerobiosis at certain rate from atmospheric oxygen availability. Specifically, Macoma balthica enlarged its survival potential up to 24.8 days (LT50) under air exposure at 12 °C as compared to other specific treatments used here (4.9 days). The latter pattern was also observed, although in a much lower magnitude, for the other intertidal species Cerastoderma edule that survived 3.7 and 4.6 days (LT50) under nitrogen atmosphere and anoxic seawater incubation, respectively as compared to 9.5 days for emersed individuals. In contrast to the subtidal species, aerial exposure of both intertidal species led to a much higher survival performances than incubation of individuals in anoxic media with the presence of antibiotic. Survival capacity of the subtidal species Mytilus edulis and Spisula subtruncata was statistically similar under air and nitrogen atmospheres and anoxic seawater incubation. Then, subtidal species have a limited ability to air breathing as a conclusion of a similar survival in atmospheric and anoxic seawater incubations. Remarkably, M. edulis represented the only exception when considering longer-term survival capacity compared to the LT50 values. Indeed, differences in LT90 values for M. edulis were statistically different, values decreasing significantly from 19.7–19.9 days (under both nitrogen and air atmospheres) to 16.7 days when individuals are incubated in anoxic seawater. This may be due to the adverse effects of anaerobic bacteria that spontaneously proliferate within the static seawater incubations. As well as for S. subtruncata, possible aerobic processes under aerial exposure of mussels seemed to be not significant for the enlargement of its survival potential, since results obtained for both air and nitrogen atmospheres are similar. Pre-treatment with the antibiotic chloramphenicol caused survival capacity to increase by a factor of approx. 2 (M. edulis) and 34–44% (S. subtruncata). In contrast to intertidal species, the direct addition of the antibiotic to the incubation media caused the highest survival performances in both subtidal species. Habitat differences and species-dependent variability must be considered as significant sources of variation when studying the anaerobic performance of individuals using the most common experimental anaerobic techniques to test survival potential

Micronuclei (MN), nuclear buds (NB), fragmented-apoptotic (FA) and bi-nucleated (BN) cells were analysed in gills of bivalve mollusks Macoma balthica and Mytilus edulis collected from fi ve study locations in Lithuanian territorial waters of the Baltic Sea. Th e frequency of micronuclei varied from 1.28 to 3.63‰ (MN/1000 cells), of nuclear buds – from 0.50 to 1.49‰, fragmented-apoptotic cells from 0.53 to 1.72‰ and of bi-nucleated cells from 1.51 to 2.23‰. Th e highest level of MN and bi-nucleated cells was determined in mollusks from the off shore Station 65, nuclear buds and fragmented-apoptotic cells from Station 1B located close to the Būtingė oil terminal. A comparatively high frequency of MN was observed in bivalves from the Būtingė oil terminal area – 3.38‰ in Station 1B, 2.85‰ in Station B06 in June and in mollusks from Station N-4 (2.66‰) located nearby the oil platform D-6.

We investigated the effects of two functionally different deposit feeders, the amphipod Monoporeia affinis and the bivalve Macoma balthica, on the benthic emergence of copepods (Acartia spp., Eurytemora affinis, Temora longicornis), cladocerans (Bosmina longispina maritima, Daphnia spp.), and rotifers (Synchaeta spp., Keratella spp., Notholca spp.) in the northern Baltic Sea. We performed 3.5-week laboratory experiments in June-July and in September-October using surface sediment containing zooplankton eggs and various combinations of amphipod and bivalve densities. Both zoobenthic species increased egg mortality rates in Synchaeta spp. and in calanoids. Each amphipod consumed a maximum of one Synchaeta spp. egg and 31 calanoid eggs per day, while the bivalves consumed six Synchaeta and 143 calanoid eggs per day. Monthly consumption throughout the community matches or even exceeds the field densities of eggs. In summer, M. affinis decreased the daily emergence rate of Synchaeta spp. by 31-53% and of M. balthica by 57%. The effect on calanoids was less severe: the emergence rate of Acartia spp. and E. affinis was significantly suppressed only by M. balthica (the reduction was 48% and 28% in Acartia spp. and in E. affinis, respectively). T. longicornis was the only species that benefited from macrofauna: together the two zoobenthic species resulted in a 2.7-fold increase in the emergence of this calanoid. Bioturbation significantly influences the benthic emergence of zooplankton, with effects varying among species, and may thus affect the dynamics of pelagic populations.

Spatial variations in benthic macrofaunal species composition, abundance and biomass in estuarine intertidal habitats have been often related to such environmental variables as salinity, sediment types and tidal depth. However, there have been few attempts to investigate the relations between such macrobenthic parameters and intertidal beach width gradient in order to predict their likely responses to coastal squeeze induced by accelerating sea-level rise in an estuarine environment. This article investigates the linkages between environmental variables and patterns in the distribution, abundance and biomass of estuarine intertidal macrobenthos in order to provide a basis for describing the effect of future sea-level rise in the Humber estuary, UK. Field surveys were conducted in September 2003 and 2004 over a variety of spatial scales based on a hierarchically scaled field study (system: 105 m; region: 105–104 m; local 104–103 m; transect: 103–102 m; station; 102–101 m) along two focal environmental gradients: (1) the longitudinal gradient (length of the estuary) over an entire estuarine system and (2) the beach width gradient (varying beach width altered by historic land-claim) over a sub-area of the estuary. Statistical analysis was carried out in order to identify key environmental variables and the most relevant spatial scales that best explain the observed spatial variability in macrobenthic biomasses. At the system scale, the dominant species were two bivalves Cerastoderma edule and Macoma balthica and a polychaete Nereis diversicolor, which accounted for 51.7%, 25.0% and 12.1%, respectively, of the total biomass. At the regional scale, univariate analysis showed clear trends in species richness, abundance and biomass along the longitudinal and beach width gradient. At the transect scale, multiple regression analysis revealed that the variances in biomass of M. balthica, C. edule and other remaining species as well as total macrobenthic biomass were largely explained (54–98%) by the key environmental variables, such as salinity, organic matter content, beach width and beach slope. At the station scale, the degree of variability explained by the environmental variables was markedly lower along beach width gradient (8–32%) than along longitudinal gradient (34–77%), but the analysis revealed a significant role of tidal depth along both gradients at this spatial scale. Overall, intertidal habitats with higher macrobenthic biomass were significantly positively related to higher salinity, muddier sediments, wider beach and shallower beach slope. This article indicates that such areas are currently situated around the lower and outer regions of the estuary where extensive shallow muddy intertidal areas can be found, but they will also be most susceptible to the impacts of sea-level rise due to their outer location and the shallowness of the beach in the Humber estuary.

In the North Sea, during autumn-winter, intertidal flats often receive a massive influx of migratory shorebirds (wildfowl, waders and seabirds), which utilise the high prey densities that are available. The present study was conducted at Culbin Sands lagoon, NE Scotland, in 1994-1996, to investigate benthic invertebrate standing stock, and the energy flow from benthic invertebrates to shorebirds. Benthic invertebrate standing stock was estimated to be 500 kJ m-2 yr-1, and shorebird consumption efficiency to be 18% of the available standing stock. A series of manipulative field experiments were then conducted to test the effects of shorebirds on benthic invertebrate densities and community structure. Birds were excluded from caged areas (exclosures), and benthic invertebrate densities (total and by class size) in caged and uncaged areas were compared for each season separately. During autumn-winter, especially the gastropod Hydrobia ulvae and larger-sized (>15 mm) clams Macoma balthica were observed to be the most impacted species, being significantly more abundant in bird-exclosures than in bird-accessed areas. En el mar del Norte, durante otono-invierno, las llanuras intermareales sufren la afluencia masiva de aves migratorias (anatidas, limicolas y aves marinas) que utilizan las elevadas densidades de presas disponibles. El presente estudio fue llevado a cabo en la laguna de Culbin Sands, en el noreste de Escocia, durante los anos 1994 a 1996 a fin de investigar la biomasa de invertebrados marinos y el flujo de energia desde los invertebrados bentonicos a las aves costeras. La biomasa de invertebrados bentonicos fue estimada en 500 kJ m-2 yr-1, y la eficiencia de consumo por parte de las aves costeras como el 18% de la biomasa disponible. Una serie de experimentos de campo manipulativos fue llevada a cabo para determinar los efectos de las aves costeras sobre las densidades de invertebrados bentonicos y sobre la estructura de la comunidad. Las aves fueron excluidas de areas cerradas a su acceso. Las densidades de invertebrados bentonicos (totales y por clase de talla) en areas cerradas y abiertas a su acceso fueron comparadas por separado para cada estacion del ano. En otono-invierno, el gasteropod Hydrobia ulvae y ejemplares de gran talla (>15 mm) del bivalvo Macoma balthica fueron las especies que sufrieron un mayor impacto, siendo significativamente mas abundantes en zonas cerradas que en zonas abiertas al acceso de las aves.

In this study we report on the occurrence and potential significance of Atlantic sturgeon (Acipenser oxyrhynchus) feeding traces observed in the Bay of Fundy in great abundance on the intertidal mud flats of Mary's Point, New Brunswick, Canada. The traces comprise a crescent-shaped impression and a plug-shaped excavation and are considered to be a modern analogue for the trace fossil Piscichnus. Local areas exhibit relatively great numbers of the feeding structure: the sediment in these zones contains bivalves (primarily Macoma balthica), worms (generally nereid polychaetes), and amphipods (Corophium volutator). Analysis of the feeding-trace distribution and orientation shows that activity is greatest within 500 m of mean high water and coincides with the highest population densities of amphipods (up to 30,000 individuals per m2). Where sturgeon feeding is most intense, voluminous quantities of clay and silt are redistributed. Within the study area, as much as 1,220 m3 of intertidal sediment is r...

A main molecular subdivision in the circumpolar Macoma balthica complex has been described between Atlantic and Pacific taxa. In NE Europe, the clams of the White and Barents Seas, however, show deviant genetic structures. Using allozyme and mitochondrial DNA data, we explore the hypothesis that these deviations result from hybridization between an Atlantic (M. b. rubra) and an invading Pacific (M. b. balthica) lineage. A practically pure Atlantic Macoma extends from France north to the Varanger Peninsula (NE Norway), whereas populations farther east have genetic compositions intermediate between true Atlantic and true Pacific. Admixture estimates range from 32 to 90% Pacific contribution, with a notable deviation in a nearly pure Atlantic outpost in the Mezen Bay (NE White Sea). The pattern of variation is not one of a simple collinear mixing however. Different characters exhibit different degrees of introgression, and the relative introgression varies regionally. Yet, there are practically no interlocus genotypic disequilibria between the diverged loci, which brings out the White Sea-Barents Sea M. balthica as the best-documented marine animal hybrid swarms so far, arisen through amalgamation of genomes previously isolated since pre-Pleistocene times. On top of the main admixture pattern, strong geographical structuring is also seen in characters unrelated to the principal systematic distinction. The persistence of the regional patterns indicates restricted gene flow at the present time, despite the high dispersal potential of the species. The causes of this structuring could be in a complex history of colonization events and features of local hydrography enhancing isolation and divergence of populations.

In estuarine areas, bivalve species can be found in a variety of environments, where they experience large differences in environmental conditions. In the present paper, the importance of different habitats (intertidal, subtidal and adjacent coastal waters) for the persistence of the population was evaluated for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea estuary. Intra-specific variation in growth and reproductive output were followed during the year and related to local abiotic conditions. Significant differences in growth and reproductive investment were found between locations. Young individuals were mostly found in the intertidal area, where growth in terms of somatic mass was good. These areas were not favourable for adult individuals, since growth in shell length was low and many individuals did not reproduce. In the subtidal, where the highest densities were found, somatic and gonadal mass indices were low. Coastal areas had the lowest densities and showed high growth in terms of shell length and body mass. The habitat with the highest reproductive effort per individual was not the most important habitat in terms of reproductive output due to differences in density and in size of the habitat type. For M. balthica, the subtidal habitat contributed the most to the reproductive output of the western Dutch Wadden Sea population although the highest reproductive output per individual was in the coastal area.

In controlled laboratory transmission experiments, uniform doses of axenic in vitro isolate cultures of Perkinsus marinus from a Crassostrea virginica oyster, and of independent P. chesapeaki isolates from Chesapeake Bay Mya arenaria and Macoma balthica clams, were used to reciprocally challenge Perkinsus sp.-free C. virginica, M. arenaria, and M. balthica experimental hosts. Following mantle cavity inoculations, all 3 experimental hosts acquired high incidences (30 to 100%) of infections by each of the 3 Perkinsus sp. isolates, based on PCR assays of DNAs from exper- imental host tissues that were collected through 60 d post-inoculation. Lesions containing proliferat- ing pathogen cells were documented histologically in tissues of all experimental host species chal- lenged with all isolates of both Perkinsus species. Experimental Perkinsus sp. challenge isolates were re-isolated and propagated in vitro from infected tissues of host molluscs from most (5 of 9) experi- mental treatment groups. Koch's postulates were generally satisfied to confirm experimental infec- tions in all bivalve molluscs that were challenged with 3 isolates of 2 Perkinsus spp. These results suggest potential broad and overlapping host specificities for the 2 current Chesapeake Bay-endemic Perkinsus species: P. marinus and P. chesapeaki.

The aims of the study were to determine the contents of glycogen, organic carbon and nitrogen in the Baltic clam Macoma balthica tissue and to find out whether there is any difference in fitness and chemical composition between individuals living in sediments with different pore-water hydrogen sulphide concentrations. It was found that hydrogen sulphide permanently present in the sediment at concentrations exceeding 513 μmol dm −3 at the middle depths of the Gulf of Gdansk (60 m) had no adverse influence on the fitness of M. balthica and did not reduce the organic compound content in its tissue. This is very probably because of the presence of oxygen in the near-bottom water. Interestingly, animals living in such concentrations of hydrogen sulphide had heavier shells and a greater soft tissue weight. Moreover, the contents of organic matter and glycogen in their soft tissues were significantly higher. Glycogen was 30% higher on average, ranging from 11.1 to 30.3% AFDW during the year. At all the stations during the year, organic carbon in M. balthica tissue varied from 50.3 to 55.2% AFDW, and organic nitrogen from 7.7 to 11.7% AFDW.

A series of 27 successive annual estimates of production of soft parts of the bivalve Macoma balthica (L.) populating the tidal flats of Balgzand (western Wadden Sea, The Netherlands) was obtained using multi-station (15 sites) and long-term (27 yr: 1978 to 2004, inclusive) monitoring data on numerical densities and ash-free dry mass (AFDM). Annual production values were esti- mated from seasonal growth increments, which were positive in spring and early summer and (in adults) negative in the remainder of the year, when up to 70% of individual weight gain of the preceding growing season was lost. Annual estimates based on twice-annual sampling were checked and refined on the basis of a detailed 2 yr study. Weight loss proportions increased with age of ani- mals and with water temperature in winter. Net annual somatic production of the entire population varied from 1 to 9 (27 yr mean: 2.9 ± 0.3) g AFDM m -2 yr -1 . Lifetime production per individual averaged 0.007 g AFDM for recruits of ~3 mo old and 0.032 g AFDM for ~10 mo olds. Numerical den- sities of ~10 mo old recruits predicted, within narrow limits, subsequent cohort production by way of a positive linear relationship. However, production of 3 mo old recruits was on average higher at low than at high densities, owing to better juvenile survival at low densities. Local (between-station) variation in mean annual production was primarily related to local variation in recruitment. However, production per recruit was significantly higher at low than at high intertidal levels, in accordance with higher growth and lower mortality rates at lower levels. Strong temporal and local variation was also found in annual production/biomass (P/ - B) ratio values, which reflected the variable age compo- sition of the population: P/ - B ratio values were augmented whenever mean age was low. Consistently higher mean P/ - B ratio values (~0.6 vs. ~0.4 yr -1 ) were found at high near-coast compared with low off-shore tidal flats, in accordance with higher mortality rates on high flats. Environmental factors affecting variation in annual production included between-year variability in recruitment (which was related to winter temperature and shrimp predation pressure) and growth (which was related to diatom abundance).

Blooms of the brevetoxin-producing Karenia brevis in the Gulf of Mexico cause massive fish kills, food poisoning and adverse respiratory effects in humans. Sedimentation of toxic cells following inert clay application could reduce toxin incorporation by commercially important suspension-feeding bivalves and thus prevent direct public health impacts, but could potentially lead to brevetoxin (PbTx) accumulation by benthic deposit-feeders. The goal of this study was therefore to compare suspension- and deposit-feeding as pathways for brevetoxins. We investigated: (1) the effect of toxic K. brevis on both feeding modes using a facultative deposit-suspension feeding tellinid bivalve, the clam Macoma balthica, as a model species and (2) the relative effectiveness of brevetoxin transfer via suspension- and deposit-feeding over 24-h exposure. Sedimentation of K. brevis was achieved by treatment with 0.25 g phosphatic clay l-1 and brevetoxin concentrations were measured by ELISA. Karenia brevis reduced both suspension- and deposit-feeding activity. This study demonstrates that brevetoxins can be rapidly accumulated by a surface deposit-feeding bivalve from sedimented K. brevis cells and that comparable toxin levels can be attained by both suspension- and deposit-feeding modes [1.2–1.6 µg PbTx (g tissue wet weight)-1]. Deposit-feeding clams generally do not pose a direct threat to humans but may provide a pathway for brevetoxin food web transfer.

Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass ( Spartina alterniflora × Spartina foliosa ) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C 4 plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ 13 C and δ 15 N) composition of the clam Macoma petalum (= M. balthica ) among native marsh, hybrid Spartina , and mudflats in central San Francisco Bay. We found higher densities (individuals m −2 ) of M. petalum on mudflats compared to either native or hybrid Spartina ( p Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 ( p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ 13 C but not δ 15 N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina . Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa , despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C 4 carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum .

We report the application of a recently developed molecular method, single step nested multiplex PCR (SSVM-PCR) assay and microscopy to identify and investigate temporal patterns of bivalve larvae in a Danish estuary, Isefjord. All samples were collected during the SUSTAINEX program from June to November 2001. Using the molecular assay, larvae could be categorized into six groups: the blue mussel, Mytilus edulis, Ensis spp., species of the Myoidae superfamily (Mya spp.), the common cockle (Cardiidae family), members of the Abra and Macoma genera of the Tellinoidae superfamily and members of the surf clam genera, Spisula spp. A seventh group was composed of unknown larvae. Greater resolution was possible by microscopy, but only for relatively large and intact individuals (>150-200 μm). The molecular approach was capable of differentiating between larvae regardless of shell size. Where it was possible to directly compare identifications based on both methods, concordance was high for M. edulis, Macoma balthica/Abra alba and E. americanus, whereas identification of Myoidae spp. and Cardiids was less consistent. Over the course of the study, two patterns of larval occurrence were observed. Larvae from species known to exhibit a protracted annual spawning period (M. edulis, Myoidae spp., Mysella bidentata and Cardiids) were present in the water column throughout the sampling period, whereas larvae of Abra alba, Barnea candida, E. americanus, Macoma balthica, Musculus marmoratus Scrobicularia plana and Tapes pullastra appeared at clearly defined periods.

The causal links between species traits and bioaccumulation by marine invertebrates are poorly understood. We assessed these links by measuring and modeling polychlorinated biphenyl bioaccumulation by four marine benthic species. Uniformity of exposure was achieved by testing each species in the same aquarium, separated by enclosures, to ensure that the observed variability in bioaccumulation was due to species traits. The relative importance of chemical uptake from pore water or food (organic matter, OM) ingestion was manipulated by using artificial sediment with different OM contents. Biota sediment accumulation factors (BSAFs) ranged from 5 to 318, in the order Nereis virens < Arenicola marina ≈ Macoma balthica < Corophium volutator. Calibration of a kinetic model provided species-specific parameters that represented the key species traits, thus illustrating how models provide an opportunity to read across benthic species with different feeding strategies. Key traits included species-specific differentiation between (1) ingestion rates, (2) ingestion of suspended and settled OM, and (3) elimination rates. The high BSAF values and their concomitant variability across the species challenges approaches for exposure assessment based on pore water concentration analysis and equilibrium partition theory. We propose that combining multienclosure testing and modeling will substantially improve exposure assessment in sediment toxicity tests.

Marine litter is one of the problems marine ecosystems face at present, coastal habitats and food webs being the most vulnerable as they are closest to the sources of litter. A range of animals (bivalves, free swimming crustaceans and benthic, deposit-feeding animals), of a coastal community of the northern Baltic Sea were exposed to relatively low concentrations of 10 μm microbeads. The experiment was carried out as a small scale mesocosm study to mimic natural habitat. The beads were ingested by all animals in all experimental concentrations (5, 50 and 250 beads mL− 1). Bivalves (Mytilus trossulus, Macoma balthica) contained significantly higher amounts of beads compared with the other groups. Free-swimming crustaceans ingested more beads compared with the benthic animals that were feeding only on the sediment surface. Ingestion of the beads was concluded to be the result of particle concentration, feeding mode and the encounter rate in a patchy environment.

Since her shipwreck in 1771, the wooden vessel Vrouw Maria has been lying on the seabed at 41. m depth on the border between the Archipelago Sea and the northern Baltic proper, off the southern coast of Finland. The wreck lies in an upward position in a right angle to the dominating bottom current, which is potentially affecting seabed topography, sediment characteristics and zoobenthic communities both upstream (NE) and downstream (SW) of the wreck. This multidisciplinary study attempts to clarify abiotic and biotic patterns and processes in the vicinity of the wreck by combining field investigations with physical simulation studies in the field and in the laboratory. Multibeam echo-sounder techniques were utilised to generate a map of the wreck area and sediment grab samples were taken to characterize the sediment type and its zoobenthic community. A medium-sized field experiment generated data on the accumulation of sediment organic matter in the presence and absence of a current and/or a barrier on the seafloor and a small-scaled laboratory study was conducted to simulate scour forming processes. The results showed that a deeper basin, scour area, with the dimensions 150×300m, was present downstream of the wreck and there was also a smaller scour area upstream of the wreck. Similar traces on the bottom were simulated in the laboratory. The organic content (recent mud) and the proportion of finer sediment were more pronounced in areas closer to both sides of the wreck. These results were in turn imitated in a field experiment, where the accumulation of organic matter in the sediment increased significantly downstream, when a current was interrupted by a barrier. Regarding zoobenthos in the wreck area, 11 taxa and a mean total abundance of 773 individuals per m2 were registered. The dominant species were Macoma balthica and Marenzelleria sp., which together made up >80% of the total number of individuals. Multivariate data analyses showed significant differences in community structure between upstream and downstream sides of the wreck and these differences were basically expressed as more individuals upstream of the wreck of the seven most common species. Univariate data analyses also showed significantly more species and higher total abundance in the scour area upstream of the wreck compared to the downstream scour area. The weakened communities downstream of the wreck were possibly due to accumulation of organic matter and more frequent occurrence of hypoxia. The results are useful for describing bottom areas around long-term physical barriers/artificial reefs, as background measurements ahead of possibly increased archaeological diving activities, sediment excavations or measures taken to raise the wreck to the surface, as well as for any attempts to preserve the wreck in situ.

We simulated growth and size-selective predation mortality of juvenile Wadden Sea bivalves, predicted size distributions of prey Macoma balthica shaped by their predators Crangon crangon (Brown shrimp), and compared these predictions with observations in the field. Under the assumption that all mortality is caused by shrimp, size-selective predation could explain bivalve size structure in several cases with quite realistic and consistent prey choice functions. In about half of the 14 studied time periods, bivalve size structures could not be reproduced by selective shrimp predation, but unselective mortality never led to a reliable fit of the field data. We conclude that size-dependent abundance changes are the rule in the early life of these bivalves. Various size-dependent processes such as migrations could affect local abundances. The results strongly support that a major determinant of young M. balthica abundance and size distribution of the survivors is predation by shrimp.

At what phenotypic level do closely related subspecies that live in different environments differ with respect to food detection, ingestion, and processing? This question motivated an experimental study on rock sandpipers (Calidris ptilocnemis). The species' nonbreeding range spans 20 degrees of latitude, the extremes of which are inhabited by two subspecies: Calidris p. ptilocnemis that winters primarily in upper Cook Inlet, Alaska (61°N), and C. p. tschuktschorum that overlaps slightly with C. p. ptilocnemis but whose range extends much farther south (∼40°N). In view of the strongly contrasting energetic demands of their distinct nonbreeding distributions, we conducted experiments to assess the behavioural, physiological, and sensory aspects of foraging, and we used the bivalve Macoma balthica for all trials. Ptilocnemis consumed a wider range of prey sizes, had higher maximum rates of energy intake, processed shell waste at higher maximum rates, and handled prey more quickly. Notably, however, the two subspecies did not differ in their abilities to find buried prey. The subspecies were similar in size and had equally sized gizzards, but the more northern ptilocnemis individuals were 10-14% heavier than their same-sex tschuktschorum counterparts. The higher body mass in ptilocnemis likely resulted from hypertrophy of digestive organs (e.g. intestine, liver) related to digestion and nutrient assimilation. Given the previously established equality of the two subspecies' metabolic capacities, we propose that the high-latitude nonbreeding range of ptilocnemis rock sandpipers is primarily facilitated by digestive (i.e. physiological) aspects of their foraging ecology rather than behavioural or sensory aspects.

Bakalaura darbā pētīta baltijas plakangliemeņu (Macoma balthica) populācijas ģenētiskā daudzveidība Rīgas jūras līča piekrastes zonā. Izmantojot iPBS (inter - Primer Binding Sequences) metodi veikta 12 dažādu atradņu gliemeņu ģenētiskās daudzveidības analīze. PCR amplifikācijas produkti, pēc reakcijas ar diviem praimeriem (2232 un 2394), tika analizēti agarozes gēlā. Kopā tika konstatēti 38lokusi. Darbā analizētajiem paraugiem konstatēts augsts polimorfisma līmenis. Salīdzinot atradnes savā starpā, polimorfu lokusu skaits - 22 (59 %). Ģenētiskā līdzība visām populācijām ir augstāka par 88 %. Iegūtie dati tika matemātiski apstrādāti ar POPGENE un NTSYS programmnodrošinājumu., The work is devoted for the detection of genetic diversity in population of Baltic tellin Macoma balthica in shore of Gulf of Riga. Using iPBS method 12 populations were analyzed for genetic diversity and adjustments of method was made. A total of 240 tissue samples were collected. DNA of 60 good quality samples was analyzed. PCR amplification products by reaction with two primers (2232 and 2394) were analyzed in agarose gel and analyzed with POPGENE and NTSYS software. Total of 38 loci were identified. High level of polymorphism was determined. Comparing the findings with each other, there were 22 (59 %) polymorphic loci found. Genetic similarity for all populations is higher than 88%.